Russian Flying Helmet Conversion

Posted January 2002
Updated February 2009
Updated February 2013

Note:
This
article is the one I originally wrote when I converted my Russian
helmet to aircraft use. I've since switched away from speakers in
the ear cups, using IPOD ear buds instead. Details for these
changes, including details on how to build the adaptor, are given on
the Russian
Helmet Part Two page.

Last week, my wife gave me a Russian military leather flying helmet
for Christmas. I was surprised at the quality of the helmet, and
decided
to try convert it for use in my Fly Baby. You can find these
helmets from a variety of places.

Anyway, the first step was to try to get it to fit me a bit better.
It was a metric size 56, about a size 7, and I generally wear about 7
3/8.
It had a thick fleece lining, though, and since I didn't need it for
warmth,
I figured it could be removed to give me a little more room.

While the back end was held in by snaps, close examination showed
the
sides and front were stitched in. The stitches were through all the
layers,
so I couldn't just cut the stitching or the outside leather shell edge
would be rough. The fleece's backing was thin, though, and cut easily
with
a seam ripper. I cut out the fleece, and the fit was good.

While I was doing fabric work, I cut the seam holding the
head-cushion
in place. It's a good idea on a canopy airplane, but wasted on an
open-cockpit
machine. Plus, it looks stupid. Turns out it isn't really a cushion;
it's
more of an indexing mark for when a hard helmet is worn over the
leather
one. The cushioning inside the helmet has a notch in it to fit the tab
atop the leather one.

Now for the earphones. The helmet had two cords fitting out the
back,
one with a broad four-conductor connector and the other with a slim
two-conductor
one. Two conductors on the big connector were the only ones that showed
anything less than infinite resistance. A quick check with a battery
resulted
in clicks from the ear cups, so I knew those were the headphones.

Things were a bit weird in the resistance department. I had expected
that the earsets would be either 8-ohm commercial impedance or the
~300-ohm
aviation standard. The DC resistance was over 3,000 ohms!

I have an old Escort 110 in my office for listening to local
traffic.
I connected up the headset lines and clip-leaded them to the Russian
headset.
It worked, but the volume was low. I had picked up the Rat Shack 1000:8
center-tapped audio transformer in case it had proved out to be eight
ohms.
I patched that in place, with no improvement.

So it appeared I would have to replace the speakers themselves. The
insides of the ear cups had a thin layer of foam with a 3/4" hole for
the
speakers. I carefully cut away the thin foam to reveal a rubber
membrane
holding the speaker units in place. A few second's work with a small
screwdriver
as a lever, and the unit popped out.

It was small...about 1.5" deep, and about 3/4" deep. I was a bit
concerned
about finding a speaker element that small. I went to Rat Shack. They
had
2" tweeters (for about $25 a set) but nothing smaller. See
Update Below.

I considered whether I might get the tweeters to work...but decided
to keep looking for one the closer size. I knew I could probably find
something
by mail or at the professional-level electronics stores, but this was
Sunday
and I wanted to get something working.

One thing that occurred to me is that the ear units from a
Walkman-style
headset might work. I looked at them, but they were rated only for
about
.1 Watt. I knew I would be operating at a fairly high level, so needed
a heavier-duty speaker.

So, I went to Goodwill Aerospace. There, I found a decrepit set of
Realistic
headphones for $2, and another Rat Shack headset that had a built-in
radio
for the same amount.

To home, to disassemble the prizes. The headphones' speakers were
2",
and looking at the headset, it was obvious they wouldn't work. I took
apart
the integrated headphones/radio unit...and found two 1.5" speakers.

So, I soldered the headset wiring to the speakers and popped them
behind
the membrane. Chasing down the wiring, I found the original speakers
had
been series-wired. I reworked the wiring to make them parallel. The
cheap
headphones had included a long cord and a 1/4" phono plug, so I was all
set.

Microphone-wise, I had been intending to cannibalize a cheap
aviation
headset I bought several years ago. But when I opened it up, I found
some
sort of transistor network on the microphone line. I didn't really want
to switch that whole mess over, so I decided to take a look at
alternatives.

I dropped by the aviation parts store on Friday, and found a
complete
Flightcom boom mike replacement set. This was the parallel-wire sort of
boom, and all it needed for installation was a small hole for a #8
screw.
It cost $60, but included the cable and connectors and everything. The
nice thing was, I wouldn't have to do ANY electrical work...all it
needed
was a mount.

The forward part of each ear cup on the helmet included a pair of
small
studs used to hold the hooks that the oxygen mask attached to. I
removed
one of the hooks and cut out a small piece of ~0.090" aluminum that fit
the stud pattern and had a tab area for the mike mounting screw.
Installing
the boom was pretty staightforward. I strung the cable from the mike
through
a convenient leather loop at the back of the helmet, then tie-wrapped
it
to the earphone cable.

This afternoon, I gave it a try. The first thing I noticed is that
the
left headset output was a bit distorted...a bit of a buzz when people
transmitted.
Signal came in nice and clear, though. Probably a bad speaker.

The noise attenuation seems to be about the same as my old
non-noise-cancelling
headphones, or maybe just a tad worse. The exterior of the ear cups is
just a bit of hard rubber, there is no noise-attenuating foam inside.

However, I was able to fly with the headset volume NOT at the
maximum...on
my old headset, I always had to fly with the volume up all the way.

The big advantage was comfort...it completely eliminated the
head-compressing
effect of a standard set of headphones. It also eliminated much of the
low-frequency rumble (from the prop blast hitting the exteriors of the
ear cups) that neither my old headset nor my noise-attenuating one seem
to be to handle.

I did try it with foam earplugs in place, but, again, they worked a
bit too well on the incoming transmissions as well. I had to operate
with
the volume all the way up, and concentrate on what is being said.

It short...it didn't work half bad. I'm still not sure if I'm going
to give up my ANL unit for it. It's nice to get the low frequencies
lessened,
but radio clarity (and volume level) are really better with my Denalis.

But anyway, such a conversion is a viable alternative. I probably
have
less than $150 into the thing, which included a brand-new Flightcom
microphone
boom. And it looks a heck of a lot better than the usual commercial
helmet/headset
combination. I'll probably buy a set of brand-new speakers and see how
they work out.

[Note: Talking to people afterwards, I probably should have tried
the
Russian speakers in the helmet before changing them out...they probably
would have worked just as well. They do need to be changed from series
to parallel wiring as described above, though]

Hardware
Sources: February 2013

I got email from John Thryd in Australia. He converted his
Russian helmet after finding two replacement speakers. He pointed
me to a company in US called Rugged
Radios, who sells speakers
that appear to fit the Russian Helmet. You want to buy the 300
ohm speakers and connect them in parallel.